It was beyond the muscular humanoid demon's expectation that his own wariness of the rune formations being thrown out by the unknown rune master had made him essentially fall into the runemaster's trap.
Due to the placement of the pillars of dark flames that blocked his way and supposedly a trap to lure him into another disadvantageous position, turned out to be just another deadly trap that he had successfully failed to get out of due to his inability to sense the extra rune formations that were thrown before the rune formations were about to manifest themselves.
So when the muscular humanoid demon took a step back to dodge the single rune formation he saw with his two eyes, he failed to notice the other two that had activated behind his back.
The two rune formations that were almost placed directly behind the muscular humanoid demon then flashed before manifesting the spell contained inside them.